The invention relates to a linear bearing which can be suitably used in an apparatus which performs rotational and reciprocal motions, such as a polishing apparatus for a semiconductor.
Conventionally, a linear bearing such as shown in FIG. 2 is used. The linear bearing comprises a sleeve 52 which supports a shaft 51 via balls 56. Spline grooves 53 and 54 are formed in the shaft 51 and the sleeve 52, respectively, and the balls 56 are arranged between the spline grooves 53 and 54. A retainer 55 which retains the balls 56 is urged by coil springs 57 from both the sides in the axial direction.
When a force in the axial direction acts on the shaft 51 to move the shaft 51, the balls 56 on the spline grooves 53 and 54 roll along the spline grooves 53 and 54, and the retainer 55 moves in the axial direction together with the balls 56 against the urging force of the coil springs 57.
However, the linear bearing of the prior art has the following problem. The shaft 51 can reciprocally move in the axial direction. When a force for rotating the shaft 51 in the circumferential direction is applied to the shaft 51, however, the shaft 51 cannot rotate in the circumferential direction because the balls 56 cannot move in the circumferential direction beyond the spline grooves 53 and 54.